Method for forming a free wound electromagnetic deflection yoke

ABSTRACT

A free-wound electromagnetic yoke is formed by winding the X-axis with a continuous piece of heat bondable wire wound around a plurality of coil forms positioned on a mandrel and turned by a lathe. After winding, the mandrel is heated to cause the windings to form solid coils. After cooling, the solid coils are removed from the mandrel and from the coil forms. The same process is repeated for the Y-axis. The solid coils for both the X-axis and the Y-axis are placed in a toroidal support ring to form an electromagnetic yoke.

This is a divisional application of U.S. application Ser. No. 08/460,419filed on Jun. 2, 1995, now issued as U.S. Pat. No. 5,631,615.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to electromagnetic lenses andyokes and, more particularly, to a simplified method for winding thecoils of electromagnetic lenses and yokes.

2. Description of the Prior Art

Yokes and electromagnetic lenses are widely used in electron beam tools,electron microscopes, and cathode ray tubes (CRTs). Yokes and lensesemploying toroidal magnetic deflection coils are commonly used electronbeam lithography systems for focusing an electron beam on to a substratefor submicron patterning of semiconductor devices.

U.S. Pat. No. 4,251,728 to Pfeiffer shows an example of a toroidalmagnetic deflection yoke. The operation of such a yoke is fairlystraightforward. Opposing rectangular windings are arranged in a circleto form a toroid. For example, FIG. 1A shows one pair of opposing coils,10 and 10', arranged at opposite sides of a circle 12 forming a toroidalyoke. Typically, one of these coils controls the electron beamdeflection in the Y direction and the other coil in the X direction. Inoperation, a deflection current is passed through the coils from point Ato point B through interconnection 14. The deflection current travels ina direction specified by the arrows I_(o) and I_(i). Magnetic fields 16are created in each leg of the coils in a direction prescribed by thewell-known right-hand rule. An electron beam 18 traveling through thecenter of the toroid, between opposing legs of the coils, is influencedby the aggregate of the magnetic fields 16 and deflected to a new path18'.

FIG. 1B a shows a sectional view of the windings shown in FIG. 1A takenalong line 2-2'. It can be seen that the electron beam 18 can bedeflected in either direction by controlling the deflection currents inthe coils 10 and 10'.

Presently, electromagnetic coils are formed by winding wire intomultiple radial cut grooves cut on a plastic form. The method used forwinding the form to make the coils is characterized as being difficultand time consuming. Proper winding requires alternating between the Xand the Y windings. As the number of radial cut grooves and the numberof turns increases, so does the degree of difficulty and the timeinvolved.

FIG. 2 shows a top view of a traditional toroidal yoke. A plastic formhaving slots numbered from 1 to 19, starting at the twelve o'clockposition and counting counter clockwise, form both the X and Y coil axeswhich make up the toroidal yoke. FIG. 3 shows the toroidal yoke of FIG.2, opened up along line 3-3'. As is readily apparent, the windingprocess is quite involved. Referring now collectively to FIGS. 2, 3, and4A-D, the recommended winding procedure is as follows:

Step 1. Take three spools no larger than 1.5 inches in diameter and wrap130 inches of 20 AWG wire onto each of two spools. Label the first spool"X1" and the second spool "X2". Wrap 240 inches of 20 AWG wire onto thethird spool and label it spool "Y".

Step 2. Take the spool labeled "X2" and unwrap three inches of wire andlabel the end "X2 Start". Beginning at slot No. 19 wrap according to theview shown in FIG. 4D. Tape the wire to the form.

Step 3. Take the spool labeled "Y" and unwrap six inches of the wire andlabel the end "Y Start". Beginning at slot No. 18, wrap according to thewinding style shown in FIG. 4A. Continue to wrap in a counter clockwisedirection to slot No. 20 according to the winding style shown in FIG.1A. Repeat this for slots Nos. 1 and 2. Tape the wire to the form.

Step 4. Take the "X2" spool and go counter clockwise to slot No. 17 andwrap according to the winding style shown in FIG. 4C. Repeat this forslots Nos. 16 and 15. Tape the wire to the form.

Step 5. Take the "X1" spool and unwrap six inches of wire and label theend "X Start". Beginning at slot No. 3, wrap according to the windingstyle shown in Figure shown in FIG. 4D. Tape the wire to the form.

Step 6. Take the "Y" spool and go counter clockwise to slot No. 4wrapping according to the style shown in FIG. 4A. Now bring the spoolclockwise to slot No. 14 and wrap according to the winding style shownin FIG. 4B. Tape the wire to the form.

Step 7. Take the "X2" spool and go clockwise to slot No. 13 wrappingaccording to the winding style shown in FIG. 4C. Bring the spool counterclockwise to slot No. 1. Remove the wire from the spool and label it "XReturn".

Step 8. Take the "Y" spool and go counter clockwise to slot No. 12wrapping according to the winding style shown in FIG. 4B. Repeat thisfor slot Nos. 11 and 10. Put a spacer into slot No. 9 at this point. Thespacer should be two layers of wire, three rows wide. Take the "Y" spoolclockwise to slot No. 8 and wrap according to the winding style shown inFIG. 4B. Take the spool counter clockwise to slot No. 16. Remove thewire from the spool an label it "Y return".

Step 9. Take the "X1" spool and go counter clockwise to slot No. 5wrapping according to the winding style shown in FIG. 4D. Repeat thisfor slots Nos. 6 and 7. Remove the spacers from slot No. 9. Remove thewire from the spool. Take the wire and thread it into slot No. 9according to the winding style shown in FIG. 4D. Take the end of thewire clockwise to the space between slot No. 1 and slot No. 20. Stripboth this and the end of the wire labeled "X2 Start" about 0.38 inchesapart. Put a one inch length of heat shrink tubing onto the wire labeled"X1" and overlap the wire ends 0.38 inches. Solder these wires togetherand cover joint with shrink tubing.

Step 10. Take "X Start" to slot No. 16 and label it "X Drive". Twist ittogether with "X Return".

Step 11. Take "Y" to slot No. 1 and label it "Y Drive". Twist ittogether lightly with "Y return".

This process is time consuming and prone to mistakes. For instance, asthe number of turns goes up, so does the degree of difficulty and timeinvolved. Keeping uniform tension on the wires and keeping the wirestraight is also a difficult task. Any slack or tangling results in anunbalanced, non-functioning yoke. Cooling is also a problem with thistype of wound yoke since, at best, only about 30% of the coil areafacing away from the plastic form is accessible to a cooling medium.This results in poor, unbalanced cooling. For high power applicationsthis situation is unacceptable since the increased amounts of heat thatis generated will adversely effect yoke performance.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide asimplified method for winding a toroidal yoke.

It is yet another object of the present invention to provide a freewound yoke where the X axis and a Y axis are wound separately.

It is yet another object of the present invention to provide a yokewhich can be more efficiently cooled.

A free wound toroidal yoke is formed using a reusable mandrel mounted toa lathe. The mandrel is essentially a straight shaft. Coil windingfixtures for either the X or the Y axis are slid on to the mandrelseparated from each other with spacers and ejector plates. A starter endof bondable wire is affixed to the first winding fixture and held taut.By turning the lathe manually to rotate the mandrel, the wire begins towind around the first fixture in a uniform fashion. When the requisitenumber of winds is wound around the first fixture, the wire is pulledover to the second fixture and again the lathe is rotated until therequisite number of winds is reached. This procedure repeated for eachof the fixtures on the mandrel until the last fixture is wound. When thewinding is complete there is one complete axis, either the X or the Y,comprised of a number of individual coils all wound with a continuouspiece of bondable wire. The entire mandrel assembly is then heated in anoven to bond the coiled wire to form solid coils. The same procedure isperformed for the remaining axis. Once cooled, the coil fixtures areslipped off of the mandrel and the solid coils are removed from thefixtures via the ejector plates. The coils for both the X and the Y axesare placed into a slots around a toroid shaped support ring to form anelectromagnetic yoke.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, in which:

FIG. 1A is prior art showing two opposing coils in a typical toroidalyoke;

FIG. 1B is a sectional view of the coils shown in FIG. 1A taken alongsectional line 2-2';

FIG. 2 is a prior art toroidal yoke winding;

FIG. 3 is the prior art toroidal yoke shown in FIG. 2 opened up alongline 3-3' illustrating the complicated winding pattern for both the Xand the Y axes;

FIGS. 4A-4D are winding styles required to form the prior art yoke shownin FIGS. 2 and 3;

FIG. 5 is an isometric view of the toroidal yoke according to thepresent invention;

FIG. 6 is a top view of the toroidal yoke according to the presentinvention;

FIG. 7 is a sectional view taken along line 4-4' of FIG. 6;

FIG. 8 is a view of a winding mandrel used to form free woundelectromagnetic coils;

FIG. 9 is a view of the winding mandrel having fixtures comprising acomplete axis for the toroidal yoke;

FIG. 10 is a view of a winding fixture taken along line 5-5' of FIG. 9.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 5, there isshown an isometric view of the free wound yoke according to the presentinvention. Only one half of the yoke is shown for illustrative purposes.The yoke is comprised of individual free wound coils 10 affixed in anouter toroidal support ring 12 and an inner toroidal support ring 14.Corresponding slots 16 in the outer ring 12 and the inner ring 14 holdthe free wound coils 10 in place. For illustrative purposes, the coilscomprising the X-axis are shaded while the coils comprising the Y-axisare not.

FIG. 6 shows a top view of the free wound toroidal yoke comprised oftwenty coils. The X-axis is comprised of coils labeled X1 through X10.Likewise, the Y-axis coils are comprised of coils labeled Y1 throughY10. Arrows on the coils indicate the direction of the wind. All of theX-axis coils are formed from a continuous strand of wire with the startof the wire labeled "X-Start" at coil X1, and the end of the wirelabeled "X-End" at coil X10. Similarly, all of the Y-axis coils areformed from a continuous strand of wire with the start of the wirelabeled "Y-Start" at coil Y1, and the end of the wire labeled "Y-End" atcoil Y10.

FIG. 7 shows a sectional view taken along line 4-4' of FIG. 6. Theindividual coils 10 fit into the outer toroidal ring 12 and an innertoroidal ring 14 and are aligned with an alignment fixture 16 secured toa base plate 18. The Y-axis coils are connected via Y-interconnect wire22 and the X-axis coils are connected together via X-interconnect wire24. Since the coils are free wound, they can be placed in the supportrings, 12 and 14, so that the coil wind goes in either direction. Thearrows on the coils 10 indicate the direction of the wind. Theindividual coils 10 are fixed in place with an epoxy 20.

Turning now to FIG. 8, there is shown a reusable mandrel 30 used forwinding the free wound coils. The mandrel is essentially a long shaft 32having a adaptor 34 at one end designed to fit into a lathe (not shown).The opposite end of the shaft has a threaded portion 36 for securing anut 38.

The method for winding the free-wound coils is shown with reference toFIG. 9 which shows all of the winding fixtures 40, in this example tenfixtures number from left to right, comprising a complete axis, eitherthe X-axis or the Y-axis. The winding fixtures 40 are evenly spacedalong the shaft 32 of the mantle 30. A more detailed view of the windingfixture 40 is shown in FIG. 10. In the preferred embodiment, a spool 42of 20 gage bondeze wire is used. A starter end of bondable wire isaffixed to the first winding fixture and held taut in a wire groove 44.As the lathe begins to rotate the mandrel 30, the wire 46 begins to windaround the first fixture 40 in a uniform fashion. When the requisitenumber of winds is wound around the first fixture, the wire is moved tothe wire groove 47 of the second fixture and the lathe again begins torotate until the requisite number of winds is reached. For the yoke inthe present example, thirty-nine turns is used. This procedure repeatedfor each of the fixtures on the mandrel until the last fixture is wound.Arrows above each fixtures 40 indicate the direction of the wind. Asshown, starting with fixture number 6 and continuing through fixturenumber 10, the direction of the lathe, and hence the direction of thewind, has been reversed. When the winding is complete there is onecomplete axis, either X or Y, comprised of a number of individual coilsall connected with a continuous piece of wire 46.

The entire mandrel assembly 30 is then heated to bond the coiled wire.For 20 gage bondeze wire the coils 10 are baked at 100°-150° C. forabout four hours until the coils are bonded such that each coil forms asolid mass. After the coils 10 are completely cool, the nut 38 isremoved and the fixtures 40 are slid from the mandrel 30. The coils 10are then removed from their respective fixtures 40 one by one with theejector plates 50. The mandrel 30 is reusable and can be used to preformthe same procedure for the remaining axis.

The solid coils 10 for both the X-axis and the Y-axis are placed into aslots around a toroid shaped support ring to form a yoke, as shown inFIG. 6. The resultant yoke is formed of free wound coils. Unlike theprior art, keeping the wires straight is not a problem since as thefixture is revolved, it clearly exposes the next surface where the wireis to be laid. This make it very easy to keep the wire straight and tokeep uniform tension on the wire. Further, the yoke formed by thismethod allows for more uniform cooling since there is no plastic formthrough the center of the coils and approximately 90% of the coilssurfaces can be exposed to a cooling medium.

While the invention has been described in terms of a single preferredembodiment, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

We claim:
 1. A method for winding electromagnetic coils for anelectromagnetic yoke, comprising the steps of:attaching one end of acontinuous length of wire to a first coil form of a plurality of coilforms positioned along an elongated shaft; rotating said elongated shaftto wind said continuous length of wire around said first coil form toform an electromagnetic coil; attaching said continuous length of wireto an adjacent coil form positioned on said elongated shaft; rotatingsaid elongated shaft to wind said continuous length of wire around saidadjacent coil form to form another electromagnetic coil; repeating saidstep of attaching said continuous length of wire and said step ofrotating said elongated shaft for each of said plurality of coil formspositioned along said elongated shaft in order to form additionalelectromagnetic coils from said continuous length of wire; removing eachof said coil forms from said elongated shaft; and ejecting saidelectromagnetic coils formed from said continuous length of wire fromsaid coil forms.
 2. A method for winding electromagnetic coils for anelectromagnetic yoke, as recited in claim 1 further comprising the stepof heating said elongated shaft prior to said step of removing to causesaid electromagnetic coils to bond into a solid mass.
 3. A method forwinding electromagnetic coils for an electromagnetic yoke as recited inclaim 2 wherein said step of heating is at 100 to 150 degrees Celsius.4. A method for winding electromagnetic coils for an electromagneticyoke as recited in claim 1 further comprising the steps of:holding tautsaid continuous length of wire in a groove in an outer circumferentialsurface of said first coil form while winding said electromagnetic coil;holding taut said continuous length of wire in another groove in anouter circumferential surface of said adjacent coil form while windingsaid another electromagnetic coil; and repeating said step of holdingsaid continuous length of wire while forming said additionalelectromagnetic coils from said continuous length of wire.
 5. A methodfor winding electromagnetic coils for an electromagnetic yoke as recitedin claim 1 wherein said electromagnetic coils are further separated fromone another by ejector plates on said elongated shaft, said ejectorplates eject said electromagnetic coils from said coil forms.
 6. Amethod for forming a free wound toroidal electromagnetic yoke,comprising the steps of:attaching one end of a first length of wire to afirst coil form of a plurality of coil forms positioned along anelongated shaft; rotating said elongated shaft to wind said first lengthof wire around said first coil form to form an electromagnetic coil;attaching said first length of wire to an adjacent coil form positionedon said elongated shaft; rotating said elongated shaft to wind saidfirst length of wire around said adjacent coil form to form anotherelectromagnetic coil; repeating said step of attaching said first lengthof wire and said step of rotating said elongated shaft for each of saidplurality of coil forms positioned along said elongated shaft in orderto form additional electromagnetic coils from said first length of wire;heating said elongated shaft to cause said electromagnetic coils tobond; removing each of said coil forms from said elongated shaft aftersaid heating step; ejecting said electromagnetic coils from said coilforms; and affixing said electromagnetic coils in a toroidal supportring.
 7. A method for forming a free wound toroidal electromagnetic yokeas recited in claim 6, further comprising the steps of:attaching one endof a second length of wire to a first coil form of a plurality of coilforms positioned along said elongated shaft; rotating said elongatedshaft to wind said second length of wire around said first coil form toform an electromagnetic coil; attaching said second length of wire to anadjacent coil form positioned on said elongated shaft; rotating saidelongated shaft to wind said second length of wire around said adjacentcoil form to form an electromagnetic coil; repeating said step ofattaching said second length of wire and said step of rotating saidelongated shaft for each of said plurality of coil forms positionedalong said elongated shaft in order to form additional electromagneticcoils from said second length of wire; heating said shaft to cause saidelectromagnetic coils to bond; removing each of said coil forms fromsaid elongated shaft after said heating step; ejecting saidelectromagnetic coils from said coil forms; and affixing saidelectromagnetic coils in said toroidal support ring, saidelectromagnetic coils formed from said first length of wire forming afirst axis of said electromagnetic yoke and said second length of wireforming a second axis of said electromagnetic yoke.
 8. A method forforming a free wound toroidal electromagnetic yoke as recited in claim 7wherein winding direction for said electromagnetic coils is determinedaccording to the direction of rotation of said elongated shaft.
 9. Amethod for forming a free wound toroidal electromagnetic yoke as recitedin claim 6 further comprising the steps of:holding taut said firstlength of wire in a groove in an outer circumferential surface of saidfirst coil form while winding said electromagnetic coil; holding tautsaid first length of wire in another groove in an outer circumferentialsurface of said adjacent coil while winding said another electromagneticcoil; and repeating said step of holding said first length of wire whileforming said additional electromagnetic coils from said first length ofwire.
 10. A method for forming a free wound toroidal electromagneticyoke as recited in claim 6 wherein said electromagnetic coils arefurther separated from one another by ejector plates on said elongatedshaft, said ejector plates eject said electromagnetic coils from saidcoil forms.